People with prediabetes, who are at risk of developing type-2 diabetes, have blood glucose levels somewhere between normal and diabetic, researchers said. Blood glucose can be directly tested in several ways, but these tests only provide a snapshot. To get a picture of blood glucose levels over time, doctors test for levels of glycated hemoglobin, or A1c, in the blood.

“Our study supports the idea that the A1c test, used to diagnose type-2 diabetes, can also be used at a much earlier stage to screen for the disease in the high risk population, like overweight patients,” said Dr Nataly Lerner of Tel Aviv University’s Sackler Faculty of Medicine.

When blood glucose levels are high, more A1c is formed. So A1c serves as a biomarker, indicating average blood glucose levels over a two- to three-month period. The A1c test has long been used to monitor type-2 diabetes. And in the past few years, the American Diabetes Association (ADA) and World Health Organisation have added the test to their guidelines as a criterion for diagnosing type-2 diabetes, researchers said.

According to the ADA, having an A1c level of 6.5 per cent or more is an indicator of the disease and an A1c level of between 5.7 and 6.4 per cent is an indicator of prediabetes.

The test is simpler to administer than the most common blood glucose tests, requiring neither fasting nor consuming anything. The findings were published in the European Journal of General Practise.